Thermodynamics of polymer mixtures

In the form of solutions, polymers find use in paints and other coating materials. They are also used in lubricants (such as multigrade motor oils), where they temper the reduction in viscosity with increasing temperature. In addition, aqueous polymer solutions are pumped into oil reservoirs for promoting tertiary oil recovery. In these applications, the polymer may witness a range of temperatures, pressures, and shear rates, and this variation can induce phase separation. Such a situation is to be avoided and it can be, with the aid of 

In addition, polymer thermodynamics is very important in the growing and commercially important area of selecting components for polymer-polymer blends. There are several reasons for blending polymers  

By varying the composition of a blend, the engineer hopes to obtain a gradation in properties that might be tailored for specific applications. This is true for miscible polymer pairs such as polyphenylene oxide and polystyrene that appear and behave as single-component polymers. 

If one of the components is a commodity polymer, its use can reduce the cost or, equivalently, improve the profit margin for the more expensive blended product 

In this chapter, we present the classical Flory-Huggins theory, which can explain a large munber of observations regarding the phase behavior of concentrated polymer solutions. The agreement between theory and experiment is, however, not always quantitative. Additionally, the theory cannot explain the phenomenon of phase separation brought about by an increase in temperature. It is also not very useful for describing polymer-polymer miscibility. For these reasons, the Flory-Huggins theory has been modified and alternate theories have been advanced, which are also discussed. 

Suppose a single phase has a composition 0o- At equilibrium the system finds a state of minimum free energy, so, if there existed a pair of compositions 01 and 02 such that, if the system separated into two phases at these compositions, the total energy were lowered, then the single phase at composition 0o 

The Flory-Huggins theory is in fact nothing more than a two-component polymer version of the simple lattice gas model introduced in section 2. We divide the free energy into an entropic part, which is assumed to take the simplest perfect gas form, while the enthalpic part is estimated using a typical mean-field assumption. 

We saw in section 2.4 that the entropy of mixing of a polymer of degree of polymerization N and holes was given by an expression of the form 

Exactly the same expression would hold for a polymer and a solvent. If instead 

The translational entropy associated with each chain is reduced by a factor of N to reflect that monomers in the same chain are connected and cannot be positioned independently. 

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Discussion To What Extent is the Statistical Thermodynamics of Polymer Mixtures and Block Copolymer Melts Understood ... 

Traditionally, the thermodynamics of polymer mixtures was developed in terms of a lattice model, with each monomer unit of the polymer chains occupying a single lattice site. The free energy of mixing of polymers in solution can be described by the Flory-Huggins equation ... 

THERMODYNAMICS OF POLYMER MIXTURES FACTORS AFFECTING MISCIBILITY IN POLYMER BLENDS... 

In this work we will discuss some further aspects of the thermodynamics of polymer mixtures such as the effect of pure component properties on polymer-polymer miscibility, the influence of pressure on the LOST, and the influence of polydispersi-ty on the phase behavior of polymer mixtures. 

Thermodynamics of Polymer Mixtures Table 9.1 UCST Data for Solutions of PS in DOP... 

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